In highly industrialized areas the state and local regulations concerning industrial wastewater discharge in the existing municipal sewers or water bodies are very stringent thus making the cost of industrial wastewater pretreatment very high. Many industrial manufacturers must install and operate local wastewater pretreatment systems which due to their high cost along with the discharge permit fees adversely affect the cost of products. Sometimes the local environmental protection regulations could result in industrial manufacturers having to go out of business. Re-use of the treated effluent within the industrial plant process technologies can minimize the use of potable water resulting in decrease in the cost of permits for wastewater discharges, and, possibly, could eliminate the permit fee completely. Further, even when treated wastewater effluent quality meets the regulatory requirements the discharges could hydraulically overload the existing municipal sewerage and treatment plants. Recycling has been the only practical alternative for increased discharge capacity at local community wastewater treatment plants. Recycled water may be used for spray irrigation of golf courses, public parks and county property, and for make-up water for boilers. Likewise, natural water sources can also be contaminated in its ambient condition with industrial wastes and require more efficient purification.
The main goal of this invention is to develop a cost-effective and efficient method and apparatus for treating contaminated water including natural and industrial wastewater which results in obtaining high purity effluent usable for recycling. The known methods of obtaining high purity effluent from heavily contaminated industrial wastewater are generally based on sequencing particular treatment facilities in a complex treatment train or sequence which usually results in relatively high capital and operational costs of the system. There are known multi-functional treatment systems in which various processes are combined in a reduced number of treatment units.
It is known that treatment of industrial wastewater is provided more cost-effectively and efficiently when high purity effluent usable for recycling results from the treatment. In order to obtain high purity effluent, inorganic and organic suspended solids, oily globules and emulsions, colloidal and dissolved matter, and trace elements should be removed. Total Suspended Solids (TSS) and oily globules have been removed by upward stream and downward stream gravity separation mostly enhanced by adding coagulation and/or flocculation means. In this technology, gravity separation is provided either by sedimentation (downward stream), or by flotation (upward stream), or by filtration. The latter can be implemented either in buoyant or fixed filter media, or in liquid-liquid or liquid-solids fluidized beds. The biodegradable and eventually low-biodegradable organic colloidal and dissolved substrates are biologically oxidized. The non-biodegradable organic colloidal and dissolved substrates are removed by adsorption. The trace elements are removed by ion exchange or by membrane methods.
In many stages of treatment some additives which enhance the liquid-solid separation processes can be used, particularly to enhance coagulation and/or flocculation, such as synthetic organic flocculants. Depending upon the nature and concentration of wastewater impurities the flocculants could be cationic, anionic or non-ionic polymers. Traditional industrial wastewater treatment systems which use combinations of different polymers and/or adsorbents specified for different contaminants consist of sequencing treatment units for each reagent, thus resulting in complex and cost-ineffective treatment plants. For relatively large treatment systems, complex multi-stage treatment plants could be justified. However, for smaller installations the complexity of the treatment systems is a major problem.
On the other hand, the method of treating industrial wastewater by the present invention is based on optimum combinations of various reagents to result in new combined reactive admixtures with an enhanced cumulative action. In fact, the combined reactive admixtures are themselves new reagents. The combination of reagent components results in creation of a new reagent which can cumulatively treat different wastewater impurities, thereby permitting creation of a correspondingly combined packaged treatment apparatus. The total cost of a combined treatment process-apparatus complex unit is much less than the total cost of separate units for separate treatment processes.
The following is a brief description of the known in the art combined process-apparatus complex units.
U.S. Pat. No. 3,929,640 (Dohnert) describes a water treating apparatus incorporating improved mixing and flow mechanisms. The apparatus provides simultaneous water clarification and softening with coagulants and calcium hydroxide and/or soda ash which cumulatively provide removal of suspended, colloidal and dissolved matter. A corresponding hydraulic shape of the apparatus along with a plurality of nozzles through which raw water is introduced in the unit in order to provide internal recirculation, reaction and clarification. The unit is equipped with settled sludge collection and removal means. Although the apparatus has its practical advantages, a drawback is that its use is limited only to physico-chemical treatment of water and, probably, also for some industrial wastewaters. With this apparatus, it seems to be practically impossible to treat oil and grease contaminated wastewater.
A compact apparatus for the purification of wastewater by a physical-chemical treatment described in U.S. Pat. No. 4,136,012 (Louboutin et al) combines the neutralization, coagulation, flocculation, and lamellar decanting within a single unit. The system has advantages if only enhanced clarification is considered. However, it cannot provide high purity effluent since the lamellar cartridges have an increased overflow rate, thus also having a high hydraulic capacity, which does not allow high TSS removal efficiency. Another drawback of the method and of the apparatus is that it is limited to phase separation processes and cannot provide Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) removal.
U.S. Pat. No. 4,192,742 (Bernard et al) describes a process and apparatus for biological treatment by superoxygenation of wastewater followed by pressurized biological filtration. This high rate biological treatment process, however, requires separate pretreatment of wastewater in order to remove TSS and oil and grease. Also higher energy consumption can add to the cost of system operation. The described system is a sequencing combination of separate units and is rather complicated. When pretreatment and effluent polishing are required the system becomes even more complicated. Due to the above drawbacks, the described method and apparatus have limited applicability.
Another method and apparatus for the filtration of a suspension by a granular filtration layer is described in U.S. Pat. No. 4,720,347 (Berne) as an upward flow filtration enhanced with air washing and fluidization of the upper layer of filter media. The method has an advantage in its combination of granular filtration and fluidized bed filtration along with simultaneous washing the filter media is an obvious advantage of the method. However, it is applicable only for removal of suspended and colloidal matter. If a flocculation additive is used for enhancing the treatment process, it would increase the possibility of clogging the filter media, thus resulting in increase in fluidization velocities which lead to carry over the filter media. Also, a pretreatment to remove large suspended particles is required.
U.S. Pat. No. 4,547,286 (Hsiung) describes a high rate water filtration process and apparatus having an upflow filter with buoyant filter media and a downflow filter with non-buoyant filter media. The upflow filter is provided with an air washing component which decreases the density of the filter media thus resulting in expansion of the media and minimization of its hydraulic resistance. The system also has a pretreatment unit in which suspended solids are removed. Despite its advantages, it, nevertheless, has a drawback in that it includes sequencing compartments and piping which makes the system relatively complicated. Another drawback is that the system itself cannot provide efficient BOD, COD and Total Organic Carbon (TOC) removal.
U.S. Pat. No. 5,035,795 (Schmid) describes an apparatus for wastewater treatment which combines the processes of flocculation, sedimentation, aeration, sludge return, effluent collection and skimming within a single modular unit. Air lift is used for flocculant recirculation. Despite its advantages, it, nevertheless, has a drawback in that it would be difficult to adapt it for use with high molecular flocculants. Another drawback is that the system requires pretreatment for TSS and Oil and Grease (OG) removal.
U.S. Pat. No. 4,707,252 (Durot et al) describes a fluidized bed reactor for aerobic or non-aerobic biological treatment of wastewater which contains a fluidized bed of granular material. The treatment process is based on the three-phase gas-liquid-solids reactions and includes a device for removing air bubbles, a device for separation of the solid particles from the bacterial floc and from the discharged effluent, and a device for recirculating the effluent which is a means for fluidization of the bed of granular material. Despite its advantages, it, nevertheless, has a drawback in that it is a complex apparatus including many sections and compartments as well as moving parts which add to the cost of its maintenance and operation (O&M). Another drawback of the reactor could be media channeling caused by a plug-flow fluidization regime. The channeled upward flow fluidization can result in inefficient use of the fluidized bed volume.
U.S. Pat. No. 4,869,815 (Bernard et al) describes a fluid bed reactor for biological treatment of liquids which contains granular media fluidized by the liquid to be treated. To avoid channeling, the fluidized media is supported by a flow distribution granular transfer material. The transfer material would compensate for the major disadvantage of the plug-flow fluidization of the fluidized granular media with potential media channeling. However, this has the substantial drawback of making the reactor very complex.
U.S. Pat. No. 3,956,128 (Turner) describes an apparatus for treating industrial and domestic wastewater which is a cylindrical system divided into two concentric tanks, thus forming an intermediate space, considered to be an aeration chamber. Then the liquid is oxygenated under pressure and pumped through a spiral tube for reaction and for transfer of soluble impurities into insoluble suspended particles by a conventional process of biochemical oxidation. The admixture from the spiral tube is released into the central zone where the activated sludge solids rise upward due to dissolved air flotation, is then collected on the surface and returned back to the process, while the separated effluent (subnatant) is removed from the reactor. The system requires pumps and devices for saturation of the liquid with the air as well as devices for collection and removal of floated scum, making the apparatus very complex. Another disadvantage of the reactor is the spiral tube which winds outside the tank, and it is difficult and costly to construct and operate the system.
Dauthuille describes in the article (LE DENSADEG--Un Nouveau Decanteur a Hautes Performances, L'Eau, 1988, 2, 63-72) a combination of fixed film biological treatment and high-speed lamella plate separation in an advanced system which is characterized by enhanced biological oxidation for both carbon and nitrogen removal. The upward flow submersed fixed-film media filtration combined with lamella plate phase separation is a complementary apparatus providing biological removal of organic carbon and nitrogen and physical-chemical removal of suspended particles. However, the system has the drawback in that it requires backwashing the fixed-film filter media.
A biofilm airlift suspension reactor (BAS-reactor) described by Tijhuis et al. (Formation of Biofilms on Small Suspended Particles in Airlift Reactors, Water Science and Technology, 1992, 26, No. 9-11, 2015-2019) uses small particles as suspended biofilm carrier for aerobic treatment of wastewater. The reactor's hydraulic pattern contains an internal recirculation loop and a three-phase separator which is built into the reactor and is hydraulically connected with the biomass carrying recirculation loop. The biomass detachment process plays a dominant role which is a drawback since it complicates the phase separation process.
U.S. Pat. No. 4,787,978 (Nicol) describes a method for the purification of urban wastewater focused on using more concentrated activated sludge, thus increasing the efficiency of the use of the reaction volume. The increase in activated sludge concentration is achieved by separate thickening of the return sludge in a laminarization (inclined parallel plate or tube) sedimentation tank. However, when compared with the fluidized bed reactors which combine the reaction and phase separation volumes in one apparatus, this method has the substantial disadvantage of being more complicated.